The objective of this project is to determine the chemical nature and the biological role of non-pyrimidine dimer damage in ultraviolet irradiated DNA. As a probe for such damage, this study will employ a DNA-binding protein isolated from human placenta and specific for some form of non-dimer damage. Using simple synthetic polynucleotides, insight will be gained into the nature of the damage and its chemical properties. The biological role of this damage will be investigated by following its fate in UV-irradiated bacterial cells using 125I-labelled protein as a probe for the damage. This work will be extended to the various UV-sensitive bacterial mutants as well as to normal and mutant human fibroblasts growing in tissue culture.